The effect of opacifier properties on thermal conductivity of vacuum insulation panel with fumed silica
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The effect of opacifier properties on thermal conductivity of vacuum insulation panel with fumed silica Metin Davraz1 · Murat Koru2 · Hilmi Cenk Bayrakçi3 · Yusuf Yusufoğlu4 · Osman Ipek5 Received: 8 August 2019 / Accepted: 2 January 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract The reduction of radiation heat transfer in VIPs is an important issue. In VIPs, the radiation heat transfer is reduced by the use of opacifier. However, the amount of opacifier also significantly affects the cost of VIP. In this study, the effect of different types and sizes of opacifiers on VIP thermal conductivity was investigated. For this purpose, 6 VIP samples containing different opacifiers (SiC, graphite and calcium aluminate in 3 different grain sizes) were produced. Fumed silica, glass fiber and opacifier were used as fillers in VIP cores at 65%, 20% and 15% (by mass), respectively. VIP samples were vacuumed up to 0.1 Pa, and their thermal conductivity coefficients were measured according to TS EN 12667 standard. In addition, transmittance ratios (%T) of fumed silica, glass fiber, opacifiers and core samples were measured by FTIR spectrophotometer and the mass extinction coefficients of each sample were calculated. The silicon carbide (F1000) as the opacifier (e: 399 m2 kg−1) and the graphite-containing core among the VIP core samples (e: 149 m2 kg−1) exhibited the highest mass absorption coefficient. In addition, the thermal conductivity of the core samples without barrier was measured under 1 Pa vacuum and then the radiation conductivities were calculated from the obtained data. F800 type SiC significantly reduced radiation heat transfer, while the solid conduction of the core was increased due to its relatively coarse grain size. VIP sample with SiC (F1200) provided the lowest thermal conductivity at 0.1 Pa (3.94 mW mK−1). As a result, F1200 type SiC was found to be the most efficient type of opacifier among the investigated opacifiers. Keywords Vacuum insulation panel · Opacifier · Mass extinction coefficient · Thermal conductivity · Radiative conductivity
Introduction
* Murat Koru [email protected] 1
Department of Construction Technology, Senirkent Vocational School, Isparta Applied Science of University, Isparta, Turkey
2
Department of Mechanical Engineering, Technology Faculty, Isparta Applied Science of University, Isparta, Turkey
3
Department of Mechatronic Engineering, Technology Faculty, Isparta Applied Science of University, Isparta, Turkey
4
Research and Development Center, Adel Kalemcilik Tic. ve San. A.S., Kocaeli, Turkey
5
Department of Mechanical Engineering, Engineering Faculty, Suleyman Demirel University, Isparta, Turkey
Vacuum insulation panels (VIPs) are made by placing a core insulation material and a gas/moisture absorber inside of an ultra high barrier film and evacuating the air from inside of the panel. The core material with pores at 10–100 nm imparts mechanical strength and thermal insulating capacity by preventing the free flow of the gas/air molecules ther
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